Probably from bump, on the pattern of words like fractious or presumptious.

• IPA^(key): /ˈbʌmpʃəs/

• Audio (Southern England):

  (file)

• Rhymes: -ʌmpʃəs
• Hyphenation: bump‧tious

bumptious (comparative more bumptious, superlative most bumptious)

1. (UK) Obtrusively pushy; self-assertive to a pretentious extreme.
   • 1891, A[rthur] Conan Doyle, A Study in Scarlet. A Detective Story, 3rd edition, London, New York, N.Y.: Ward, Lock, Bowden, and Co., […], published 1892, →OCLC:

     […] I was still annoyed at his bumptious style of conversation; I thought it best to change the topic.

   • 1918, W[illiam] B[abington] Maxwell, chapter XXII, in The Mirror and the Lamp, Indianapolis, Ind.: The Bobbs-Merrill Company, →OCLC:

     From another point of view, it was a place without a soul. The well-to-do had hearts of stone; the rich were brutally bumptious; the Press, the Municipality, all the public men, were ridiculously, vaingloriously self-satisfied.

   • 1928, Virginia Woolf, Orlando: A Biography, London: The Hogarth Press, →OCLC; republished as Orlando: A Biography (eBook no. 0200331h.html), Australia: Project Gutenberg Australia, July 2015:

     She could stand it no longer. It was full of prying old women, she said, who stared in one's face, and of bumptious young men who trod on one's toes.

   • 1938, Norman Lindsay, Age of Consent, 1st Australian edition, Sydney, N.S.W.: Ure Smith, published 1962, →OCLC, page 140:

     No doubt of it, Edmund was at grips with that bumptious little hairy dog. They were going it at the very top note of sadistic fury, screaming and snip-snapping in such a lightning mixture of black and white murder that the eye could not follow it.